Regular physical activity is one of the most important health habits known to contribute to a variety of positive health outcomes, and is the subject of proposed legislation such as the Improved Nutrition and Physical Activity Act, which seeks to provide communities resources to improve physical activity such as through development of parks and cycling paths. However, how much park development contributes to physical activity is unknown. In partnership with community groups, we propose to evaluate a natural "experiment" in Los Angeles, in that a citizen's initiative, known as Proposition K, has been approved to spend $25 million per year for 30 years to improve at least 183 local parks. Our plan is to assess the impact of park improvements on the physical activity and health of local residents. Studies to support each of our goals will be conducted in partnership with the Department of Parks and Recreation and Neighborhood Oversight Committees, the Wilmington Coordinating Council, with whom RAND has a longstanding relationship, as well as a community based organization, the Multi-Cultural Area Health Education Center (MAHEC), whose mission is focused on improving health and wellness and reducing health disparities among Latinos. The project goals are: 1) to determine whether improvements in the quality or accessibility of parks and recreational facilities result in increases in physical activity among children and adults, 2) to determine the impact of park improvements and construction of recreational facilities on other aspects of health and functioning, and 3) to determine the cost effectiveness of Prop K in increasing physical activity and to model its probable effects on morbidity. Using principles of community based participatory research, our community partners wilt form a working committee. The committee will choose among the list of Prop K projects to be built in the next 5 years, select among a variety of possible tools to assess changes in park usage and the amount of vigorous activity occurring there, and choose survey items to study whether the improved parks result in changes in other health domains, such as mental health and social support. The working committee will also assist in finding community members to help administer surveys and conduct observations. RAND and the working committee will jointly interpret results and present findings to local authorities to inform future policy decisions.